1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be installed in an exhaust system of an internal combustion engine for air-fuel ratio control, and more particularly to an improved positioning structure of a gas sensor which works to establish a desired positional relation between two porcelain insulators within a body of the gas sensor.
2. Background Art
Gas sensors are known which are installed in an exhaust system of an automotive engine to measure, for example, the concentration of oxygen in exhaust emissions of the engine for air-fuel ratio control.
FIGS. 13(a), 13(b), and 14 show porcelain insulators 93 and 94 which are employed typically in the above type of gas sensor.
The porcelain insulator 94 retains therein a sensor element 2 vertically as viewed in the drawings. The sensor element 2 has a base portion extending outside the porcelain insulator 94. The porcelain insulator 93 is laid on the porcelain insulator 94 in alignment and covers the base portion of the sensor element 2.
The porcelain insulator 93 has formed therein a chamber within which insulating ribs 931 are formed to define contact chambers. Within each contact chamber, a contact spring (not shown) is installed which establishes an electric contact between a lead extending to an external sensor control circuit and each terminal 22 formed on the base portion of the sensor element 2.
The illustrated structure, however, may result in, as shown in FIG. 14, misalignment of longitudinal center lines 930 and 940 of the porcelain insulators 93 and 94 when joined together. This causes the porcelain insulator 93 to be shifted laterally at a contact point B, thereby resulting in a physical hit of one of the ribs 931, as indicated by A, on the sensor element 2, causing damage to the sensor element 2. This problem will be objectionable, especially in a case where the volume of the chamber of the porcelain insulator 93 is decreased in order to decrease the overall size of the gas sensor.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of a gas sensor which is designed to assure relative positioning of porcelain insulators without damage to a sensor element.
According to one aspect of the invention, there is provided a gas sensor which may be installed in an exhaust system of an automotive internal combustion engine to measure the concentration of oxygen for use in air-fuel ratio control of the engine. The gas sensor comprises: (a) a hollow cylindrical housing; (b) a sensor element having a length which includes a sensing portion and a base portion, the sensor element being disposed within the housing with the sensing portion projecting from a front end of the housing and the base portion projecting from a rear end of the housing; (c) a front cover installed on the front end of the housing to cover the sensing portion of the sensor element; (d) a base cover installed on the rear end of the housing; (e) a first hollow cylindrical porcelain insulator disposed within the base cover into which the base portion of the sensor element extends; (f) a second hollow cylindrical porcelain insulator disposed in the housing, the second hollow cylindrical porcelain insulator being abutted to the first hollow cylindrical porcelain insulator in alignment with each other; (g) contact members disposed within a chamber defined inside the first hollow cylindrical porcelain insulator, each of the contact members working to establish an electric contact between an electric terminal of the sensor element and a lead extending outside the gas sensor; and (h) a positioning mechanism working to establish a given positional relation between the first and second hollow cylindrical porcelain insulators. This achieves alignment of the first and second porcelain insulators, thus avoiding undesirable inclination of the first and second porcelain insulators relative to each other which may cause damage to the sensor element.
In the preferred mode of the invention, the first hollow cylindrical porcelain insulator is in contact of a front end thereof with a rear end of the second hollow cylindrical porcelain insulator. The positioning mechanism is made up of a protrusion formed on one of the front end of the first hollow cylindrical porcelain insulator and the rear end of the second hollow cylindrical porcelain insulator and a recess formed in the other of the front end of the first hollow cylindrical porcelain insulator and the rear end of the second hollow cylindrical porcelain insulator. The protrusion is engaged in the recess.
The contact members exert elastic pressures on the sensor element to restrain the sensor element from moving in first opposite directions. The positioning mechanism is so designed as to hold the first and second hollow cylindrical porcelain insulators from moving in second opposite directions perpendicular to the first opposite directions.
The positioning mechanism may alternatively be made up of mating portions of the first and second hollow cylindrical porcelain insulators and a mating member. The mating member is engaged in the mating portions of the first and second hollow cylindrical porcelain insulators.
The positioning mechanism may alternatively be made up of markers provided on the first and second hollow cylindrical porcelain insulators.
According to another aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow cylindrical housing; (b) a sensor element having a length which includes a sensing portion and a base portion, the sensor element being disposed within the housing with the sensing portion projecting from a front end of the housing and the base portion projecting from a rear end of the housing; (c) a front cover installed on the front end of the housing to cover the sensing portion of the sensor element; (d) a base cover installed on the rear end of the housing; (e) a first hollow cylindrical porcelain insulator disposed within the base cover into which the base portion of the sensor element extends; (f) a second hollow cylindrical porcelain insulator disposed in the housing, the second hollow cylindrical porcelain insulator being abutted to the first hollow cylindrical porcelain insulator in alignment with each other; (g) contact members disposed within a chamber defined inside the first hollow cylindrical porcelain insulator, each of the contact members working to establish an electric contact between an electric terminal of the sensor element and a lead extending outside the gas sensor, the contact members exerting elastic pressures on the sensor element to restrain the sensor element from moving in first opposite directions; and (h) a restraining mechanism working to restrain relative motion of the first and second hollow cylindrical porcelain insulators in second opposite directions traversing the first opposite directions while allowing the first and second hollow cylindrical porcelain insulators to be moved in opposite directions substantially identical with the first opposite directions.
In the preferred mode of the invention, the first hollow cylindrical porcelain insulator is in contact of a front end thereof with a rear end of the second hollow cylindrical porcelain insulator. The restraining mechanism is made up of a protrusion formed on one of the front end of the first hollow cylindrical porcelain insulator and the rear end of the second hollow cylindrical porcelain insulator and a recess formed in the other of the front end of the first hollow cylindrical porcelain insulator and the rear end of the second hollow cylindrical porcelain insulator. The protrusion is engaged in the recess.
The restraining mechanism may alternatively be made up of mating portions of the first and second hollow cylindrical porcelain insulators and a mating member. The mating member is engaged in the mating portions of the first and second hollow cylindrical porcelain insulators.